The present invention relates to weigh scale machines and in particular to an improved solid-state controller for a weigh scale machine.
Weigh scale machines of the general type to which the present invention relates are utilized for packing various products into bags or other containers at relatively high speeds (e.g., 30 bags/containers per minute) and typically comprise an infeed chute, a scale mechanism, a weigh bucket, and a discharge chute. The flow of product from the infeed chute into the weigh bucket is controlled by an adjustable flow gate. The weigh bucket is operatively connected to the scale mechanism which determines when the weight of the product in the weigh bucket is equal to the desired fill weight. Product from the weigh bucket is then dumped through the discharge chute into the bag/container when the appropriate weight is attained.
In general, the control circuitry for such weigh scale machines typically comprises a plurality of contact relays which are arranged to sequentially control the various steps in the weighing and packing process. Sequencing of the machine is generally controlled by timers which establish a predetermined delay between the performance of each successive function. Typically, the only function that is actually monitored by a sensor is the "weigh complete" function which may, for example, be monitored by a limit switch that is triggered by the scale mechanism when the weight of the product in the weigh bucket attains the desired level. The disadvantage with the use of timers, however, is that it introduces a significant limitation on the speed at which the machine can operate, since the period of each timer invariably must be set to accommodate the worse condition. In addition, controllers of this type have no way of confirming that the particular function called for has actually been performed. Thus, for example, if the dump door should fail to fully open, thereby preventing all of the product in the weigh bucket from being dispensed into the bag/container within the allotted time, the machine will erroneously underfill each bag/container without detecting the fault condition.
Thus, it is the primary object of the present invention to provide an improved weigh scale machine having a solid-state controller that includes sensors for monitoring the positions of the flow gate, the dump door, and the scale beam.
In addition, it is an object of the present invention to provide an improved weigh scale machine that is highly accurate, reliable, and capable of operating at high rates of speed.
Moreover, it is a further object of the present invention to provide an improved weigh scale machine having means for varying the rate of flow of product from the infeed chute into the weigh bucket so that the feed rate can be set in accordance with the flow characteristics of the product.
The preferred embodiment of the weigh scale machine described herein includes an infeed chute for providing product to the weigh bucket via a cylinder operated flow gate. The position of the flow gate is controlled by one cylinder in the single-stage version of the machine, and by two cylinders in the two-stage version. In the two-stage version, both cylinders are actuated to completely open the flow gate for bulk flow. However, when product weight approaches the desired fill weight, the bulk flow cylinder is deactivated, thereby partially closing the flow gate and substantially diminishing the flow rate of product into the weigh bucket. The two-stage fill capability is therefore primarily utilized when working with a product having high flow characteristics to minimize the amount of airborne product after the flow gate is completely closed. The weigh bucket has two dump doors which are operated by a single cylinder for discharging the weighed product. The weigh bucket is pivotally mounted to one end of the scale beam which has an adjustable weight mechanism connected to its other end. The fill weight necessary to cause the bucket to move down is determined by adjusting the position of the weights in the weigh mechanism in a conventional manner.
The controller for the present weigh scale machine is comprised principally of digital logic circuitry for controlling the sequencing of the various machine functions. Five magnetically-responsive sensors are utilized to monitor the positions of the dump door, flow gate and scale beam, and provide feedback signals to the logic circuitry. The control logic sequences the machine through the various functions in the weighing and packing process in response to appropriate sensor signals. In addition, the control logic controls the energization of the dump door and flow gate solenoids which in turn control the activation of the pneumatic cylinders which operate the flow gate and dump door mechanisms.
By actually monitoring the positions of the flow gate, dump door, and scale beam, the present controller is capable of optimizing the cycle time of the machine, within the limitations imposed by the flow characteristics of the product. In addition, since the controller waits for confirmation from the appropriate sensor that a commanded function has actually been performed before proceeding to the next step in the process, mechanical failures or malfunctions are almost immediately detected by the controller, thereby significantly reducing the likelihood that an appreciable number of erroneously packaged bags/containers might be processed before the fault condition is detected.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :